As a work machine used for structure demolition works, waste disposal, scrap handling, road works, construction works, civil engineering works, etc., there has been known a work machine in which an upperstructure is attached swingably to an upper portion of an travel base travelling by a power system while a multi-joint work front is attached to the upperstructure swingably in an up/down direction and front members constituting the work front are driven by actuators respectively. As an example of such a work machine, there has been a demolition work machine which is based on a hydraulic excavator. The demolition work machine includes a boom one end of which is connected to an upperstructure, an arm one end of which is connected to a distal end of the boom swingably, and a work tool such as a grapple, a bucket, a breaker or a crusher, which is attached to a distal end of the arm, so that the demolition work machine can perform a desired work.
This kind of work machine performs work while changing its posture variously in a state in which the boom, the arm and the work tool constituting the work front are stuck out of the upperstructure. For this reason, the work machine may lose its balance when an excessive work load is applied to the work machine or when the work machine performs an improper operation such as a quick motion in a state in which an overload is applied to the work machine and the front is stretched. Accordingly, various tipping over prevention techniques have been heretofore proposed for this kind of work machine.
For example, Patent Literature 1 discloses a technique as follows. That is, angle sensors are provided in a boom and an arm of a work machine respectively. Detection signals of the respective angle sensors are inputted to a control device. The control device calculates the gravity center position of the work machine as a whole and the bearing capacity of stable supporting points of an travel base in the ground surface, based on the detection signals. The value of the bearing capacity in the stable supporting points based on a result of the calculation is displayed on a display device while a warning is issued when the bearing capacity in a rear stable supporting point is not higher than a limit value for ensuring safe work.
In addition, Patent Literature 2 discloses another technique as follows. That is, sensors for detecting the posture, the motion and the work load of a machine body are provided. A model expressing present and future mechanical behavior concerned with the posture of the work machine body is constructed based on detection values of the respective sensors and with reference to a database. Determination is made as to whether the machine body will tip over or not. When tipping is predicted, a work motion in execution is stopped. Further, a motion for avoiding the tipping is started so as to prevent the tipping. When the tipping is predicted, an operator is notified of the tipping.
Further, Patent Literature 3 discloses a further technique as follows. That is, provided are angle sensors for detecting a boom angle, an arm angle, a bucket angle of a work front and a swing angle of an upperstructure, and an inclination angle sensor for detecting an inclination of a vehicle body in a front/rear direction. A static tipping moment of a work machine is calculated from detection values of the angle sensors and the inclination angle sensor and the dimensions of a predetermined portion of the vehicle body. In addition, a dynamic tipping moment generated due to a centrifugal force of swing of the upperstructure is calculated from a swing angular velocity. Further, a dynamic tipping moment generated at a sudden stop of the upperstructure is calculated from a maximum angular acceleration of the swing. A value in which one or the larger one of these two dynamic tipping moments is added to the static tipping moment is used as an tipping determination condition. The swing angular velocity is controlled when the determination condition is established.